Biosynthetic gene cluster for leptomycins

ABSTRACT

Polypeptides and domains of leptomycin polyketide synthase and the nucleic acids encoding them are provided. Methods to prepare leptomycin, leptomycin analogs, and leptomycin derivatives are described, as are methods to prepare other polyketides using the nucleic acids encoding leptomycin polyketide synthase domains or modifying enzymes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of allowed application Ser. No.10/937,730, filed 8 Sep. 2004 now U.S. Pat. No. 7,288,396, which claimsbenefit under 35 U.S.C. §119 to U.S. provisional applications No.60/502,423 (filed 11 Sep. 2003) and No. 60/553,384 (filed 15 Mar. 2004),the entire contents of each prior application being incorporated hereinby reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Grant No. 1 R43CA108372-01 awarded by the National Institutes of Health. The Governmenthas certain rights in this invention.

FIELD OF THE INVENTION

This invention relates to materials and methods for biosynthesis ofleptomycins, leptomycin derivatives and analogs, and other usefulpolyketides. The invention finds application in the fields of molecularbiology, recombinant DNA technology, chemistry, human and veterinarymedicine, and agriculture.

BACKGROUND OF THE INVENTION

Polyketides are complex natural products that are produced bymicroorganisms such as fungi and mycelial bacteria. There are about10,000 known polyketides, from which numerous pharmaceutical products inmany therapeutic areas have been derived, including: adriamycin,epothilone, erythromycin, mevacor, rapamycin, tacrolimus, tetracycline,rapamycin, and many others. However, polyketides are made in very smallamounts in microorganisms and are difficult to make or modifychemically. For this and other reasons, biosynthetic methods arepreferred for production of therapeutically active polyketides. See PCTpublication Nos. WO 93/13663; WO 95/08548; WO 96/40968; WO 97/02358; andWO 98/27203; U.S. Pat. Nos. 4,874,748; 5,063,155; 5,098,837; 5,149,639;5,672,491; 5,712,146 and 6,410,301; Fu et al., 1994, Biochemistry 33:9321-26; McDaniel et al., 1993, Science 262: 1546-1550; Kao et al.,1994, Science, 265:509-12, and Rohr, 1995, Angew. Chem. Int. Ed. Engl.34: 881-88, each of which is incorporated herein by reference.

The biosynthesis of polyketides may be accomplished by heterologousexpression of Type I or modular polyketide synthase enzymes (PKSs). TypeI PKSs are large multifunctional protein complexes, the proteincomponents of which are encoded by multiple open reading frames (ORF) ofPKS gene clusters. Each ORF of a Type I PKS gene cluster can encode one,two, or more modules of ketosynthase activity. Each module activates andincorporates a two-carbon (ketide) unit into the polyketide backbone.Each module also contains multiple ketide-modifying enzymaticactivities, or domains. The number and order of modules, and the typesof ketide-modifying domains within each module, determine the structureof the resulting product. Polyketide synthesis may also involve theactivity of nonribosomal peptide synthetases (NRPSs) to catalyzeincorporation of an amino acid-derived building block into thepolyketide, as well as post-synthesis modification, or tailoringenzymes. The modification enzymes modify the polyketide by oxidation orreduction, addition of carbohydrate groups or methyl groups, or othermodifications.

In PKS polypeptides, the regions that encode enzymatic activities(domains) are separated by linker regions. These regions collectivelycan be considered to define boundaries of the various domains.Generally, this organization permits PKS domains of different oridentical substrate specificities to be substituted (usually at thelevel of encoding DNA) from other PKSs by various availablemethodologies. Using this method, new polyketide synthases (whichproduce novel polyketides) can be produced. It will be recognized fromthe foregoing that genetic manipulation of PKS genes and heterologousexpression of PKSs can be used for the efficient production of knownpolyketides, and for production of novel polyketides structurallyrelated to, but distinct from, known polyketides (see references above,and Hutchinson, 1998, Curr. Opin. Microbiol. 1:319-29; Carreras andSanti, 1998, Curr. Opin. Biotech. 9:403-11; and U.S. Pat. Nos. 5,712,146and 5,672,491, each of which is incorporated herein by reference).

One valuable class of polyketides includes the leptomycins and theiranalogs (FIG. 1). These compounds are selective inhibitors of proteinexport from the cell nucleus and thus affect the cellular location ofproteins. The function of many key proteins and transcription factorsinvolved in cell growth can be regulated by their cellular location. Forinstance, the tumor suppressor p53 normally resides in the cell nucleuswhere its activation promotes cell-cycle arrest and apoptotic celldeath. Mislocation of p53 into the cytoplasm, especially its dominantnegative mutant forms, is associated with development of many types ofcancer. Nuclear factor κB (NFκB) is a transcriptional activator thattargets genes involved in cell proliferation and apoptosis. It isconstitutively activated in certain cancer cells, aiding tumorresistance to radiation and cancer chemotherapy drugs. NFκB resides inthe cytoplasm in an inactive form complexed with the inhibitor ofnuclear factor IκB; upon stimulation by factors such as TNF-α or CD-40ligand, events are set in place that remove IκB and allow importation ofNFκB into the cell nucleus.

Leptomycin B (LMB; also known as CI-940 or elactocin) and the ratjadones(FIG. 2) are the only known low molecular weight inhibitor of nucleartransport. Because of the structural similarities, the kazusamycins,leptofuranins and callystatins are also implicated. Callystatins comefrom a marine sponge whereas all the other compounds are bacterialmetabolites. All of these molecules are exceptionally potent, typicallydisplaying IC₅₀ values in the 100 picomolar to 10 nanomolar range.

Protein export from the cell nucleus requires a nuclear export signal(NES) as a domain in the exported protein, CRMI (exportin-1) torecognize the NES and Ran, a Ras-like GTPase. In the nucleus CRMI formsa complex with the NES-protein and Ran/GTP, then the complex istranslocated through the nuclear pore complex into the cytoplasm. There,the Ran GTPase activating protein (RanGAP), found only in the cytoplasm,promotes hydrolysis of Ran/GTP to Ran/GDP, causing release of theNES-protein.

The high potency and novel mechanism of action prompted an investigationof the antitumor activity of LMB in mouse murine and xenograph cancermodels. Activity was observed at low doses against adriamycin, amsacrineand mitoxantrone resistant P388 leukemia, other leukemias, B16 melanoma,Ridgway osteogenic and M5076 sarcomas and mammary adenocarinoma. Acutetoxicity appeared to be gastrointestinal and was exacerbated upon morefrequent or oral administration of the drug. The maximum tolerated dose(MTD) in mice ranged from 0.12 to 1 mg/kg, as a function of dosingschedule.

LMB has also attracted considerable interest as a biochemical tool tostudy the role and regulation of nucleo-cytoplasmic shuttling proteinsand for its potential therapeutic use in combination with other drugs.Vigneri and Wang, “Induction of apoptosis in chronic myelogenousleukemia cells through nuclear entrapment of BCR-ABL tyrosine kinase,”Nature Medicine (2001) 7:228-234, describes combined treatment ofcultured CML cells with STI-571 and LMB. STI-571 effectively masks theability of Bcr-AbI to be retained preferentially in the cytoplasm; uponnuclear importation of the drug-inactivated protein, LMB inhibitsnuclear export of Bcr-AbI and withdrawal of STI-571 releases the abilityof the constitutively activated AbI component to induce apoptosis. Whilethe effect of either drug alone is fully reversible (STI-571 does notpermanently inhibit Bcr-AbI and nuclear export is restored by synthesisof fresh CRM1), their combined use caused irreversible and completekilling of the Bcr-Abl transformed cells. Such treatment alsopreferentially eliminated mouse bone marrow cells that express Bcr-Abl.This strategy can overcome the main limitation of acute CML treatmentwith STI-571, which is acquired drug resistance due to mutation oroverexpression of Bcr-AbI.

LMB has other types of potential therapeutic uses. Because it canpromote nuclear retention of the p53 tumor suppressor protein, treatmentwith LMB can lead to p53 activation in the nucleus, which results incell-cycle arrest and apoptosis. Combined use LMB and actinomycin D canreactivate p53 and prevent its degradation by HPV E6 protein in cervicalcarcinoma cells infected with human papillomavirus. LMB can alsopotentiate the effect of rapamycin, an emerging cancer drug, by blockingnuclear export of mTOR, the protein kinase target of rapamycin thatcontrols the activity of two transcription factors. The antiviralactivity of LMB has been elucidated as resulting from inhibition of thenuclear export of the HIV-1 Rev protein and Rev-dependent unspliced andpartially spliced mRNA, which is an early step in viral replication. LMBinterferes with cyclinB1/Cdc2, cyclinD1/CDK4 and TGF-beta dependentsignaling also, suggesting possible uses against cancers with aberrantsignaling involving these actors. A synthetic HIV-1 Rev inhibitor,PKF050-638 (FIG. 2), has been developed that mimics the activity of LMB.

Two limitations have to be overcome to increase the potential fordevelopment of LMB into an effective anticancer or antiviral drug. One,a reliable source of pure drug must be developed, because “The use ofLMB . . . has been hampered by the variability of the quality of LMBproduction lots” (D. Daelemans et al. 2002, “A synthetic HIV-1 Revinhibitor interfering with the CRM1-mediated nuclear export” Proc. Natl.Acad Sci. USA 99: 14440-5). This is not surprising given the closestructural similarity of leptomycin-like compounds isolated from theirnatural sources (FIG. 1). In fact, at least 5 different forms ofleptomycins have been detected in the culture extracts of the ATCC 39366strain and 6 forms in another LMB producer. Two, a less toxic form ofLMB would be more appealing for drug development studies. Even thoughthe drug's effects have been reported to be fully reversible, toxicityis likely to be mechanism-related and exhibited in different bodilytissues given the widespread role of CRM1-mediated protein export. Theavailable SAR data (FIG. 2) are insufficient for designing a less toxicanalog. Analog production and evaluation will require both chemical andmicrobiological approaches, because little effort towards the totalsynthesis of LMB has been reported.

The following data suggest that analogs with an acceptable therapeuticindex could be found. LMB displayed an approx. 250-fold difference inactivity between a Rev-dependent assay and cytotoxicity to the samecells in vitro and PKF050-638 had a 75-fold difference in the same twoassays (FIG. 2). These data show that LMB itself can have a goodtherapeutic window in certain instances. It is thus likely that lesstoxic LMB analogs can be discovered as a consequence of differentialbinding to CRMI or pharmacokinetic behavior that modulates theirdistribution, half-life or metabolism.

Given the promise of leptomycin B in the treatment of conditions anddiseases characterized by undesired cellular hyperproliferation, therethus exists an unmet need for a production system that can provide largequantities of leptomycin B in a form substantially free of minorcongeners and other impurities. The present invention meets this need byproviding the biosynthetic genes responsible for the production ofleptomycins and providing for their expression in heterologous hosts.Further, there is an unmet need for analogs of leptomycins potentiallyuseful in the treatment of viral diseases. The present invention meetsthis need by providing the means for biological generation of leptomycinanalogs through genetic engineering of the biosynthetic genes.

SUMMARY OF THE INVENTION

The present invention provides recombinant nucleic acids encodingpolyketide synthases and polyketide modification enzymes. Therecombinant nucleic acids of the invention are useful in the productionof polyketides, including but not limited to leptomycin and leptomycinanalogs and derivatives in recombinant host cells.

In one aspect, the invention provides the nucleic acids involved inleptomycin biosynthesis in isolated, purified, recombinant, or syntheticform, including but not limited to sequences incorporated into a vectoror into the chromosome of a host cell. The biosynthesis of leptomycin isperformed by a modular PKS and polyketide modification enzymes. Theleptomycin polyketide synthase (herein also “leptomycin PKS” or“leptomycin synthase”) is made up of several proteins, each having oneor more modules. The modules have domains with specific syntheticfunctions.

In another aspect, the present invention provides domains and modules ofthe leptomycin PKS and corresponding nucleic acid sequences encodingthem and/or parts thereof. Such compounds are useful in the productionof hybrid PKS enzymes and the recombinant genes that encode them.

In another aspect, the present invention provides modifying genes ofleptomycin biosynthetic gene cluster in recombinant form, including butnot limited to isolated form and incorporated into a vector or thechromosomal DNA of a host cell. Such compounds are useful in theproduction of leptomycins, leptomycin analogs, and leptomycinderivatives according to the methods of the invention.

In another aspect the invention provides a recombinant PKS wherein atleast 10, 15, 20, or more consecutive amino acids in one or more domainsof one or more modules thereof are derived from one or more domains ofone or more modules of leptomycin polyketide synthase. Preferably atleast an entire domain of a module of leptomycin synthase is included.Representative leptomycin PKS domains useful in this aspect of theinvention include, for example, KR, DH, ER, AT, ACP and KS domains. Inone embodiment of the invention, the PKS is assembled from polypeptidesencoded by DNA molecules that comprise coding sequences for PKS domains,wherein at least one encoded domain corresponds to a domain ofleptomycin PKS. In such DNA molecules, the coding sequences are operablylinked to control sequences so that expression therefrom in host cellsis effective. In this manner, leptomycin PKS coding sequences or modulesand/or domains can be made to encode PKS to biosynthesize compoundshaving antibiotic or other useful bioactivity other than leptomycin.

In one embodiment, the invention provides a recombinant DNA moleculethat comprises a sequence encoding a chimeric polyketide synthasecomposed of at least a portion of the leptomycin PKS and at least aportion of a second PKS for a polyketide other than leptomycin. Suchchimeric genes are useful in the production of leptomycin analogs,leptomycin derivatives, and other polyketides.

In another aspect, the present invention provides recombinant host cellsthat contain the nucleic acids of the invention. In one embodiment, thehost cell provided by the invention is a Streptomyces host cell thatproduces a leptomycin modification enzyme and/or a domain, module, orprotein of the leptomycin PKS. Methods for the genetic manipulation ofStreptomyces are described in Kieser et al, “Practical StreptomycesGenetics,” The John Innes Foundation, Norwich (2000), which isincorporated herein by reference in its entirety. In other embodiments,the host cells provided by the invention are eubacterial cells such asEscherichia coli, yeast cells such as Saccharomyces cerevisiae, ormyxobacterial cells such as Myxococcus xanthus.

In another embodiment, the invention provides a recombinant Streptomyceshost cell that produces leptomycin in its native state, wherein at leastone domain-encoding region of the endogenous leptomycin PKS gene isdeleted, inactivated, or replaced. Also provided is a recombinantStreptomyces host cell that produces leptomycin in its native state,wherein at least one polypeptide-encoding open reading frame of theleptomycin PKS gene cluster is deleted or otherwise inactivated.

In another aspect, the invention also provides methods for producingleptomycins, leptomycin analogs and derivatives, and other polyketidesusing the nucleic acids, proteins, vectors, and host cells of theinvention.

These and other aspects of the present invention are described in moredetail in the Detailed Description of the Invention, below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows various members of the leptomycin family of naturalpolyketides.

FIG. 2 shows biological activity results for several members of theleptomycin family, and the structure of ratjadone.

FIG. 3 shows the expected organization of the leptomycin PKS and apossible pathway for biosynthesis. Biosynthetic relationships of membersof the leptomycin family are also indicated.

FIG. 4 shows the organization of the leptomycin biosynthetic genecluster as deduced from SEQ ID NO:1. FIG. 4A shows the organization ofthe portion of the gene cluster comprising LepA. FIG. 4B shows theorganization of the portion of the gene cluster comprising LepB. FIG. 4Cshows the organization of the portion of the gene cluster comprisingLepC, LepD, LepE, and LepF.

FIG. 5 shows the DNA sequence of the leptomycin biosynthetic genecluster.

FIG. 6 shows SEQ ID NO: 4, the polypeptide product of lepA, a gene inthe leptomycin PKS cluster.

FIG. 7 shows SEQ ID NO: 5, the polypeptide product of lepB, a gene inthe leptomycin PKS cluster.

FIG. 8 shows SEQ ID NO: 6, the polypeptide product of lepC, a gene inthe leptomycin PKS cluster.

FIG. 9 shows SEQ ID NO: 7, the polypeptide product of lepD, a gene inthe leptomycin PKS cluster.

FIG. 10 shows SEQ ID NO: 8, the polypeptide product of lepE, a geneencoding a cytochrome P450-type oxidase.

FIG. 11 shows SEQ ID NO: 9, the polypeptide product of lepF, a geneencoding a tetR-like transcriptional regulator.

The following references provide background on the leptomycins and arehereby incorporated by reference:

-   1) Wolff B, Sanglier J J, Wang Y. Leptomycin B is an inhibitor of    nuclear export: inhibition of nucleo-cytoplasmic translocation of    the human immunodeficiency virus type 1 (HIV-1) Rev protein and    Rev-dependent mRNA. Chem Biol. (1997) 4:139-147.-   2) Lain S, Midgley C, Sparks A, Lane E B, Lane D P. An inhibitor of    nuclear export activates the p53 response and induces the    localization of HDM2 and p53 to U1A-positive nuclear bodies    associated with the PODs. Exp Cell Res. (1999) 248:457-72-   3) Hietanen S, Lain S, Krausz E, Blattner C, Lane D P. Activation of    p53 in cervical carcinoma cells by small molecules. Proc Natl Acad    Sci USA. (2000) 97:8501-8506.-   4) Kim J E, Chen J. Cytoplasmic-nuclear shuttling of    FKBP12-rapamycin-associated protein is involved in    rapamycin-sensitive signaling and translation initiation. Proc Natl    Acad Sci USA. (2000) 97:14340-14345.-   5) Park I H, Bachmann R, Shirazi H, Chen J. Regulation of ribosomal    S6 kinase 2 by mammalian target of rapamycin. J Biol Chem. (2002)    277:31423-31429.-   6) Daelemans D, Afonina E, Nilsson J, Werner G, Kjems J, De Clercq    E, Pavlakis G N, Vandamme A M. A synthetic HIV-1 Rev inhibitor    interfering with the CRM1-mediated nuclear export. Proc Natl Acad    Sci USA. (2002) 99:14440-14445.-   7) Wang, Y, Ponelle M et al., Novel leptomycins for a Streptomyces    strain A92-308902. Inhibitors of the nucelo-cytoplasmic    translocation of the HIV-1 regulatory protein Rev. Helv Chim    Acta (1997) 80:2157-2167.-   8) Kalesse M, M. Christmann. The chemistry and biology of the    leptomycin family. Synthesis (2002) 8:981-1003.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides recombinant materials for the productionof polyketides. In one aspect, the invention provides recombinantnucleic acids encoding at least one domain of a polyketide synthaserequired for leptomycin biosynthesis. Methods and host cells for usingthese genes to produce a polyketide in recombinant host cells are alsoprovided.

The nucleotide sequences encoding leptomycin PKS domains, modules andpolypeptides of the present invention were isolated from Streptomycessp. ATCC 39366 as described in Example 1. Alternatively, the DNAsequences provided herein may be obtained through gene synthesis asdescribed in U.S. Patent Application 20040166567, which is incorporatedherein by reference. Given the valuable properties of leptomycin and itsderivatives and analogs, means to produce useful quantities of thesemolecules in a highly pure form is of great potential value. Thecompounds produced may be used as antitumor agents or for othertherapeutic uses, and/or a intermediates for further enzymatic orchemical modification, and/or as agents for in vitro inhibition ofprotein phosphatase. The nucleotide sequences of the leptomycinbiosynthetic gene cluster encoding domains, modules and polypeptides ofleptomycin synthase, and modifying enzymes, and other polypeptides canbe used, for example, to make both known and novel polyketides.

In one aspect of the invention, purified and isolated DNA molecules areprovided that comprise one or more coding sequences for one or moredomains or modules of leptomycin synthase. Examples of such encodeddomains include leptomycin synthase KR, DH, ER, AT, ACP, and KS domains.In one aspect, the invention provides DNA molecules in which sequencesencoding one or more polypeptides of leptomycin synthase are operablylinked to expression control sequences that are effective in suitablehost cells to produce leptomycin, its analogs or derivatives, or novelpolyketides.

The sequence of the leptomycin gene cluster was assembled from sequencesdeduced from the cosmids pKOS279-128.PF27, pKOS279-128.2L78, andpKOS279-130.PFA42. The gene cluster is found to comprise six openreading frames (ORFs), named lepA, lepB, lepC, lepD, lepE, and lepF. Thepolyketide synthase is encoded by lepABCD, and is comprised of elevenmodules terminating in a thioesterase domain. The lepA gene encodesmodules 0-4, where module 0 is the loading module; the lepB gene encodesmodules 5-8; lepC encodes modules 9-10; and lepD encodes module 11 andthe terminating thioesterase domain. The lepE gene encodes a cytochromeP450-type oxidase, presumably responsible for oxidation of the C24methyl group. The lepF gene appears to be a regulatory gene.

Tables 1 and 2 provide a description of genes in the leptomycin PKS genecluster including sequences encoding encoding modules, domains and ORFs,as deduced from two contigs assembled from sequences ofpKOS279-125.2L78. The nucleotide sequences of the two contigs areprovided in the attached Sequence Listing, and have been assigned SEQ IDNOS: 1 and 2, respectively.

As indicated in Table 1, the nucleic acid having SEQ ID NO:1 was foundto encode portions of two ORFs. ORF1, SEQ ID NO:6, comprises nucleotides<1 to 17260 of the SEQ ID NO:1. The start of ORF1 (LepA) lies upstreamof the beginning of SEQ ID NO:1. The nucleic acid encodes a polypeptidecomprising a portion of module 1 (a portion of KR1 and all of ACP1), andthe complete modules 2, 3, and 4 of leptomycin synthase. The sequence ofORF2 comprises nucleotides 17546 to >29467 of the SEQ ID NO:1. The endof ORF2 (LepB) lies downstream of the end of SEQ ID NO:1. The nucleicacid sequence encodes a polypeptide comprising the complete modules 5and 6 and a portion of module 7 (the beginning of KS7) of leptomycinsynthase. The modules encoded by the nucleic acid of SEQ ID NO:1 areindicated in Table 1.

Table 2 provides the ORF, module, and domain descriptions for the secondcontig, the nucleic acid of SEQ ID NO:2. One partial ORF has beenidentified, encoding a polypeptide comprising a portion of module 7(part of AT7, and all of DH7, ER7, KR7, and ACP7) and all of module 8 ofleptomycin synthase. The modules encoded by the nucleic acid of SEQ IDNO:2 and domains within each module are indicated in Table 2.

Subsequent sequencing provided the complete sequence of the leptomycinbiosynthetic gene cluster, given below as SEQ ID NO:3. The PKS modulesencoded by the nucleic acid of SEQ ID NO:3 and domains within eachmodule are indicated in Table 3. The ORFs encoding the PKS have beendesignated LepA, LepB, LepC, and LepD. LepA comprises a loading module,referred to as “module 0,” which comprises a ketosynthase domain whereinthere is a glutamine in place of the expected active-site cysteine(“KSq”), and thus likely funcations as a decarboxylase. LepD comprisesmodule 11 together with a thioesterase (TE) domain.

The LepE gene, corresponding to nucleotides 64703-65881 of SEQ ID NO:3encodes a cytochrome-P450 type oxidase. The LepF gene, corresponding tonucleotides 66124-66564 of SEQ ID NO:3 encodes a putative tetR-familytranscriptional regulator.

In another aspect of the invention, the polypeptides encoded by theabove-described leptomycin PKS genes are provided as LepA (FIG. 6; SEQID NO:4), LepB (FIG. 7; SEQ ID NO:5), LepC (FIG. 8; SEQ ID NO:6), LepD(FIG. 9; SEQ ID NO:7), LepE (FIG. 10; SEQ ID NO:8), and LepF (FIG. 11;SEQ ID NO:9). These polypeptides may be in isolated, purified, orrecombinant form, either singly or present in any combination comprisingeach other or other polyketide synthase polypeptides.

TABLE 1 ORFs, modules, and domains of the leptomycin PKS determined fromthe nucleotide sequence determined from the T3-side of the insert fromcosmid pKOS279-125.2L78 (SEQ ID NO: 1). Nucleotide feature sequencelocation Contig 1   1-29467 ORF 1   <1-17260 module 1  <1-661 KR1 <1-358 ACP1 404-661 module 2  722-6868 KS2  722-1999 AT2 2306-3352 DH23386-3991 ER2 4910-5770 KR2 5753-6571 ACP2 6611-6868 module 3 6929-12172 KS3 6929-8206 AT3 8537-9595 DH3  9629-10204 KR3 11057-11881ACP3 11915-12172 module 4 12236-17260 KS4 12236-13513 AT4 13823-14869DH4 14903-15493 KR4 16298-16807 ACP4 17003-17260 ORF2 (start) 17546->29467 module 5 17546-22879 KS5 17648-18925 AT5 19328-20299 DH520333-20932 KR5 21758-22603 ACP5 22622-22879 module 6 22961-28144 KS622961-24241 AT6 24551-25603 DH6 25652-26206 KR6 27014-27868 ACP627887-28144 module 7  28199->29467 KS7  28199->29467

TABLE 2 ORFs, modules, and domains of the leptomycin PKS determined fromthe nucleotide sequence determined from the T7-side of the insert fromcosmid pKOS279-125.2L78 (SEQ ID NO: 2). feature sequence location contig2   1-9724 ORF 2 (end)   <1->9724 module 7  <1-4501 AT7  <1-967 DH71001-1585 ER7 2528-3382 KR7 3380-4225 ACP7 4244-4501 module 8 4559-9703KS8 4559-5836 AT8 6152-7213 DH8 7250-7822 KR8 8639-9409 ACP8 9446-9703

TABLE 3 Complete list of ORFs, modules, and domains of the leptomycinPKS determined from SEQ ID NO: 3. Nucleotide feature sequence locationLepA  370-25686 module 0 KSq(0)  439-1725 AT(0) 2080-3147 ACP(0)3220-3481 module 1 3535-8844 KS(1) 3535-4812 AT(1) 5143-6204 DH(1)6241-6831 KR(1) 7759-8547 ACP(1) 8587-8844 module 2  8905-15048 KS2 8905-10182 AT2 10489-11535 DH2 11569-12147 ER2 13093-13953 KR213936-14751 ACP2 14791-15048 module 3 15109-20361 KS3 15109-16386 AT316717-17775 DH3 17809-16384 KR3 19237-20070 ACP3 20104-20361 module 420425-25449 KS4 20425-21702 AT4 22012-23058 DH4 23092-23682 KR424487-24996 ACP4 25192-25449 LepB 25735-48024 module 5 25837-31068 KS525837-27114 AT5 27427-28488 DH5 28522-29121 KR5 29947-30792 ACP530811-31068 module 6 31150-36333 KS6 31150-32430 AT6 32740-33792 DH633841-34395 KR6 35203-36057 ACP6 36076-36333 module 7 36388-42570 KS736388-37665 AT7 37981-39036 DH7 39070-39654 ER7 40597-41451 KR741449-42294 ACP7 42313-42570 module 8 42628-47772 KS8 42628-43905 AT844221-45282 DH8 45319-45891 KR8 46708-47478 ACP8 47515-47772 LepC48110-58357 module 9 48209-53437 KS9 48209-49417 AT9 49775-50824 DH950864-51454 KR9 52325-53140 ACP9 53180-53437 module 10 53501-58111 KS1053501-54781 AT10 55115-56173 KR10 56975-57637 ACP10 57854-58111 LepD58243-64173 module 11 58543-59847 KS11 58543-59847 AT11 60250-61257 KR1162143-62931 ACP11 62995-63252 TE 63253-64170

In one aspect, the invention provides an isolated or recombinant DNAmolecule comprising a nucleotide sequence that encodes at least onedomain, alternatively at least one module, alternatively at least onepolypeptide, involved in the biosynthesis of a leptomycin.

In one aspect, the invention provides an isolated or recombinant DNAmolecule comprising a sequence identical or substantially similar to atleast one of SEQ ID NOS: 1, 2, and 3 or their complement. [Hereinafter,each reference to a nucleic acid sequence is also intended to refer toand include the complementary sequence, unless otherwise stated orapparent from context.] In an embodiment the subsequence comprises asequence encoding a complete leptomycin PKS domain, module orpolypeptide.

In one aspect, the present invention provides an isolated or recombinantDNA molecule comprising a nucleotide sequence that encodes an openreading frame, module or domain having an amino acid sequence identicalor substantially similar to an ORF, module or domain encoded by SEQ IDNOS: 1, 2 or 3. Generally, a polypeptide, module or domain having asequence substantially similar to a reference sequence has substantiallythe same activity as the reference protein, module or domain (e.g., whenintegrated into an appropriate PKS framework using methods known in theart). In certain embodiments, one or more activities of a substantiallysimilar polypeptide, module or domain are modified or inactivated asdescribed below.

In one aspect, the invention provides an isolated or recombinant DNAmolecule comprising a nucleotide sequence that encodes at least onepolypeptide, module or domain encoded by SEQ ID NOs:1, 2 or 3, e.g., apolypeptide, module or domain involved in the biosynthesis of aleptomycin, wherein said nucleotide sequence comprises at least 10, 20,25, 30, 35, 40, 45, or 50 contiguous base pairs identical to a sequenceof SEQ ID NOS: 1, 2 or 3. In one aspect, the invention provides anisolated or recombinant DNA molecule comprising a nucleotide sequencethat encodes at least one polypeptide, module or domain encoded by SEQID NOS: 1, 2 or 3, e.g., a polypeptide, module or domain involved in thebiosynthesis of a leptomycin, wherein said polypeptide, module or domaincomprises at least 10, 15, 20, 30, or 40 contiguous residues of acorresponding polypeptide, module or domain.

It will be understood that SEQ ID NOS: 1, 2 and 3 were determined usingthe insert of various cosmids. Accordingly, the invention provides anisolated or recombinant DNA molecule comprising a sequence identical orsubstantially similar to a ORF encoding sequence of the insert of one ormore of these cosmids.

Those of skill will recognize that, due to the degeneracy of the geneticcode, a large number of DNA sequences encode the amino acid sequences ofthe domains, modules, and proteins of the leptomycin PKS, the enzymesinvolved in leptomycin modification and other polypeptides encoded bythe genes of the leptomycin biosynthetic gene cluster. The presentinvention contemplates all such DNAs. For example, it may beadvantageous to optimize sequence to account for the codon preference ofa host organism. The invention also contemplates naturally occurringgenes encoding the leptomycin PKS that are polymorphic or othervariants.

As used herein, the terms “substantial identity,” “substantial sequenceidentity,” or “substantial similarity” in the context of nucleic acids,refers to a measure of sequence similarity between two polynucleotides.Substantial sequence identity can be determined by hybridization understringent conditions, by direct comparison, or other means. For example,two polynucleotides can be identified as having substantial sequenceidentity if they are capable of specifically hybridizing to each otherunder stringent hybridization conditions. Other degrees of sequenceidentity (e.g., less than “substantial”) can be characterized byhybridization under different conditions of stringency. “Stringenthybridization conditions” refers to conditions in a range from about 5°C. to about 20° C. or 25° C. below the melting temperature (Tm) of thetarget sequence and a probe with exact or nearly exact complementarityto the target. As used herein, the melting temperature is thetemperature at which a population of double-stranded nucleic acidmolecules becomes half-dissociated into single strands. Methods forcalculating the Tm of nucleic acids are well known in the art (see,e.g., Berger and Kimmel, 1987, Methods In Enzymology, Vol. 152: Guide ToMolecular Cloning Techniques, San Diego: Academic Press, Inc. andSambrook et al., 1989, Molecular Cloning: A Laboratory Manual, 2nd Ed.,Vols. 1-3, Cold Spring Harbor Laboratory). Typically, stringenthybridization conditions for probes greater than 50 nucleotides are saltconcentrations less than about 1.0 M sodium ion, typically about 0.01 to1.0 M sodium ion at pH 7.0 to 8.3, and temperatures at least about 50°C., preferably at least about 60° C. As noted, stringent conditions mayalso be achieved with the addition of destabilizing agents such asformamide, in which case lower temperatures may be employed. Exemplaryconditions include hybridization at 7% sodium dodecyl sulfate (SDS), 0.5M NaPO₄ pH 7.0, 1 mM EDTA at 65° C.; wash with 2×SSC, 1% SDS, at 50° C.

Alternatively, substantial sequence identity can be described as apercentage identity between two nucleotide or amino acid sequences. Twonucleic acid sequences are considered substantially identical when theyare at least about 70% identical, or at least about 80% identical, or atleast about 90% identical, or at least about 95% or 98% identical. Twoamino acid sequences are considered substantially identical when theyare at least about 60%, sequence identical, more often at least about70%, at least about 80%, or at least about 90% sequence identity to thereference sequence. Percentage sequence (nucleotide or amino acid)identity is typically calculated using art known means to determine theoptimal alignment between two sequences and comparing the two sequences.Optimal alignment of sequences may be conducted using the local homologyalgorithm of Smith and Waterman (1981) Adv. Appl. Math. 2: 482, by thehomology alignment algorithm of Needleman and Wunsch (1970) J. Mol.Biol. 48: 443, by the search for similarity method of Pearson and Lipman(1988) Proc. Natl. Acad. Sci. U.S.A. 85: 2444, by the BLAST algorithm ofAltschul (1990) d. Mol. Biol. 215: 403-410; and Shpaer (1996) Genomics38:179-191, or by the Needleham et al. (1970) J. Mol. Biol. 48: 443-453;and Sankoff et al., 1983, Time Warps, String Edits, and Macromolecules,The Theory and Practice of Sequence Comparison, Chapter One,Addison-Wesley, Reading, Mass.; generally by computerizedimplementations of these algorithms (GAP, BESTFIT, FASTA, and TFASTA inthe Wisconsin Genetics Software Package, Genetics Computer Group, 575Science Dr., Madison, Wis.; BLAST from the National Center forBiotechnology Information at the World Wide Web (ncbi.nlm.nih.gov). Ineach case default parameters are used (for example the BLAST programuses as defaults a wordlength (W) of 11, the BLOSUM62 scoring matrix(see Henikoff (1992) Proc. Natl. Acad. Sci. USA 89: 10915-10919)alignments (B) of 50, expectation (E) of 10, M=5, N=−4, and a comparisonof both strands).

The invention methods may be directed to the preparation of anindividual polyketide. The polyketide may or may not be novel, but themethod of preparation permits a more convenient or alternative method ofpreparing it. The resulting polyketides may be further modified toconvert them to other useful compounds. Examples of chemical structuresof that can be made using the materials and methods of the presentinvention include known analogs, such as those described in Kalesse &Christmann, 2002, “The Chemistry and Biology of the Leptomycin Family”Synthesis (8):981-1003 (incorporated herein by reference) and thereferences cited therein, and novel molecules produced by modified orchimeric PKSs comprising a portion of the leptomycin PKS sequence,molecules produced by the action of polyketide modifying enzymes fromthe leptomycin PKS cluster on products of other PKSs, molecules producedby the action on products of the leptomycin PKS of polyketide modifyingenzymes from other PKSs, and the like.

As noted, in one aspect the invention provides recombinant PKS whereinat least 10, 15, 20, or more consecutive amino acids in one or moredomains of one or more modules thereof are derived from one or moredomains of one or more modules of leptomycin polyketide synthase. Apolyketide synthase “derived from” a naturally occurring PKS containsthe scaffolding encoded by all the portion employed of the naturallyoccurring synthase gene, contains at least two modules that arefunctional, and contains mutations, deletions, or replacements of one ormore of the activities of these functional modules so that the nature ofthe resulting polyketide is altered. This definition applies both at theprotein and genetic levels. Particular embodiments include those whereina KS, AT, KR, DH, or ER has been deleted or replaced by a version of theactivity from a different PKS or from another location within the samePKS, and derivatives where at least one noncondensation cycle enzymaticactivity (KR, DH, or ER) has been deleted or wherein any of theseactivities has been added or mutated so as to change the ultimatepolyketide synthesized. There are at least five degrees of freedom forconstructing a polyketide synthase in terms of the polyketide that willbe produced. See, U.S. Pat. No. 6,509,455 for a discussion.

As can be appreciated by those skilled in the art, polyketidebiosynthesis can be manipulated to make a product other than the productof a naturally occurring PKS biosynthetic cluster. For example, ATdomains can be altered or replaced to change specificity. The variabledomains within a module can be deleted and or inactivated or replacedwith other variable domains found in other modules of the same PKS orfrom another PKS. See e.g., Katz & McDaniel, Med Res Rev 19: 543-558(1999) and WO 98/49315. Similarly, entire modules can be deleted and/orreplaced with other modules from the same PKS or another PKS. See e.g.,Gokhale et al., Science 284: 482 (1999) and WO 00/47724 each of whichare incorporated herein by reference. Protein subunits of different PKSsalso can be mixed and matched to make compounds having the desiredbackbone and modifications. For example, subunits of 1 and 2 (encodingmodules 1-4) of the pikromycin PKS were combined with the DEBS3 subunitto make a hybrid PKS product (see Tang et al., Science, 287: 640 (2001),WO 00/26349 and WO 99/6159).

Mutations can be introduced into PKS genes such that polypeptides withaltered activity are encoded. Polypeptides with “altered activity”include those in which one or more domains are inactivated or deleted,or in which a mutation changes the substrate specificity of a domain, aswell as other alterations in activity. Mutations can be made to thenative sequences using conventional techniques. The substrates formutation can be an entire cluster of genes or only one or two of them;the substrate for mutation may also be portions of one or more of thesegenes. Techniques for mutation include preparing syntheticoligonucleotides including the mutations and inserting the mutatedsequence into the gene encoding a PKS subunit using restrictionendonuclease digestion. (See, e.g., Kunkel, T. A. Proc Natl Acad Sci USA(1985) 82 448; Geisselsoder et al. BioTechniques (1987) 5:786.)Alternatively, the mutations can be effected using a mismatched primer(generally 10-20 nucleotides in length) that hybridizes to the nativenucleotide sequence (generally cDNA corresponding to the RNA sequence),at a temperature below the melting temperature of the mismatched duplex.The primer can be made specific by keeping primer length and basecomposition within relatively narrow limits and by keeping the mutantbase centrally located. (See Zoller and Smith, Methods in Enzymology(1983) 100: 468). Primer extension is effected using DNA polymerase. Theproduct of the extension reaction is cloned, and those clones containingthe mutated DNA are selected. Selection can be accomplished using themutant primer as a hybridization probe. The technique is also applicablefor generating multiple point mutations. (See, e.g., Dalbie-McFarland etal. Proc Natl Acad Sci USA (1982) 79:6409). PCR mutagenesis can also beused for effecting the desired mutations. Random mutagenesis of selectedportions of the nucleotide sequences encoding enzymatic activities canbe accomplished by several different techniques known in the art, e.g.,by inserting an oligonucleotide linker randomly into a plasmid,

In addition to providing mutated forms of regions encoding enzymaticactivity, regions encoding corresponding activities from different PKSsynthases or from different locations in the same PKS synthase can berecovered, for example, using PCR techniques with appropriate primers.By “corresponding” activity encoding regions is meant those regionsencoding the same general type of activity—e.g., a ketoreductaseactivity in one location of a gene cluster would “correspond” to aketoreductase-encoding activity in another location in the gene clusteror in a different gene cluster; similarly, a complete reductase cyclecould be considered corresponding—e.g., KR/DH/ER could correspond to KRalone.

If replacement of a particular target region in a host polyketidesynthase is to be made, this replacement can be conducted in vitro usingsuitable restriction enzymes or can be effected in vivo usingrecombinant techniques involving homologous sequences framing thereplacement gene. One such system involving plasmids of differingtemperature sensitivities is described in PCT application WO 96/40968.Another useful method for modifying a PKS gene (e.g., making domainsubstitutions or “swaps”) is a RED/ET cloning procedure developed forconstructing domain swaps or modifications in an expression plasmidwithout first introducing restriction sites. The method is related to ETcloning methods (see, Datansko & Wanner, 2000, Proc. Natl. Acad. Sci.U.S.A. 97, 6640-45; Muyrers et al, 2000, Genetic Engineering 22:77-98).The RED/ET cloning procedure is used to introduce a unique restrictionsite in the recipient plasmid at the location of the targeted domain.This restriction site is used to subsequently linearize the recipientplasmid in a subsequent ET cloning step to introduce the modification.This linearization step is necessary in the absence of a selectablemarker, which cannot be used for domain substitutions. An advantage ofusing this method for PKS engineering is that restriction sites do nothave to be introduced in the recipient plasmid in order to construct theswap, which makes it faster and more powerful because boundary junctionscan be altered more easily.

In a further aspect, the invention provides methods for expressingchimeric or hybrid PKSs and products of such PKSs. For example, theinvention provides (1) encoding DNA for a chimeric PKS that issubstantially patterned on a non-leptomycin producing enzyme, but whichincludes one or more functional domains, modules or polypeptides ofleptomycin PKS; and (2) encoding DNA for a chimeric PKS that issubstantially patterned on the leptomycin PKS, but which includes one ormore functional domains, modules, or polypeptides of another PKS orNRPS.

With respect to item (1) above, in one embodiment, the inventionprovides chimeric PKS enzymes in which the genes for a non-leptomycinPKS function as accepting genes, and one or more of the above-identifiedcoding sequences for leptomycin domains or modules are inserted asreplacements for one or more domains or modules of comparable function.Construction of chimeric molecules is most effectively achieved byconstruction of appropriate encoding polynucleotides. In making achimeric molecule, it is not necessary to replace an entire domain ormodule accepting of the PKS with an entire domain or module ofleptomycin PKS: subsequences of a PKS domain or module that correspondto a peptide subsequence in an accepting domain or module, or whichotherwise provide useful function, may be used as replacements.Accordingly, appropriate encoding DNAs for construction of such chimericPKS include those that encode at least 10, 15, 20 or more amino acids ofa selected leptomycin domain or module.

Recombinant methods for manipulating modular PKS genes to make chimericPKS enzymes are described in U.S. Pat. Nos. 5,672,491; 5,843,718;5,830,750; and 5,712,146; and in PCT publication Nos. 98/49315 and97/02358. A number of genetic engineering strategies have been used withDEBS to demonstrate that the structures of polyketides can bemanipulated to produce novel natural products, primarily analogs of theerythromycins (see the patent publications referenced supra andHutchinson, 1998, Curr Opin Microbiol. 1:319-329, and Baltz, 1998,Trends Microbiol. 6:76-83). In one embodiment, the components of thechimeric PKS are arranged onto polypeptides having interpolypeptidelinkers that direct the assembly of the polypeptides into the functionalPKS protein, such that it is not required that the PKS have the samearrangement of modules in the polypeptides as observed in natural PKSs.Suitable interpolypeptide linkers to join polypeptides andintrapolypeptide linkers to join modules within a polypeptide aredescribed in PCT publication WO 00/47724.

A partial list of sources of PKS sequences for use in making chimericmolecules, for illustration and not limitation, includes Avermectin(U.S. Pat. No. 5,252,474; MacNeil et al., 1993, IndustrialMicroorganisms: Basic and Applied Molecular Genetics, Baltz, Hegeman, &Skatrud, eds. (ASM), pp. 245-256; MacNeil et al., 1992, Gene 115:119-25); Candicidin (FRO008) (Hu et al., 1994, Mol. Microbiol. 14:163-72); Epothilone (U.S. Pat. No. 6,303,342); Erythromycin (WO93/13663; U.S. Pat. No. 5,824,513; Donadio et al., 1991, Science 252:675-79; Cortes et al., 1990, Nature 348: 176-8); FK-506 (Motamedi etal., 1998, Eur. J. Biochem. 256: 528-34; Motamedi et al., 1997, Eur. J.Biochem. 244:74-80); FK-520 (U.S. Pat. No. 6,503,737; see also Nielsenet al., 1991, Biochem. 30:5789-96); Lovastatin (U.S. Pat. No.5,744,350); Nemadectin (MacNeil et al., 1993, supra); Niddamycin(Kakavas et al., 1997, J. Bacteriol. 179:7515-22); Oleandomycin (Swan etal., 1994, Mol. Gen. Genet. 242:358-62; U.S. Pat. No. 6,388,099; Olanoet al., 1998, Mol. Gen. Genet. 259:299-308); Platenolide (EP Pat. App.791,656); Rapamycin (Schwecke et al., 1995, Proc. Natl. Acad. Sci. USA92:7839-43); Aparicio et al., 1996, Gene 169:9-16); Rifamycin (August etal., 1998, Chemistry & Biology, 5:69-79); Soraphen (U.S. Pat. No.5,716,849; Schupp et al., 1995, J. Bacteriology 177: 3673-79);Spiramycin (U.S. Pat. No. 5,098,837); Tylosin (EP 0 791,655; Kuhstoss etal., 1996, Gene 183:231-36; U.S. Pat. No. 5,876,991). Additionalsuitable PKS coding sequences remain to be discovered and characterized,but will be available to those of skill (e.g., by reference to GenBank).

The leptomycin PKS-encoding polynucleotides of the invention may also beused in the production of libraries of PKSs (i.e., modified and chimericPKSs comprising at least a portion of the leptomycin PKS sequence. Theinvention provides libraries of polyketides by generating modificationsin, or using a portion of, the leptomycin PKS so that the proteincomplexes produced by the cluster have altered activities in one or morerespects, and thus produce polyketides other than the natural leptomycinproduct of the PKS. Novel polyketides may thus be prepared, orpolyketides in general prepared more readily, using this method. Byproviding a large number of different genes or gene clusters derivedfrom a naturally occurring PKS gene cluster, each of which has beenmodified in a different way from the native PKS cluster, an effectivelycombinatorial library of polyketides can be produced as a result of themultiple variations in these activities. Expression vectors containingnucleotide sequences encoding a variety of PKS systems for theproduction of different polyketides can be transformed into theappropriate host cells to construct a polyketide library. In oneapproach, a mixture of such vectors is transformed into the selectedhost cells and the resulting cells plated into individual colonies andselected for successful transformants. Each individual colony has theability to produce a particular PKS synthase and ultimately a particularpolyketide. A variety of strategies can be devised to obtain amultiplicity of colonies each containing a PKS gene cluster derived fromthe naturally occurring host gene cluster so that each colony in thelibrary produces a different PKS and ultimately a different polyketide.The number of different polyketides that are produced by the library istypically at least four, more typically at least ten, and preferably atleast 20, more preferably at least 50, reflecting similar numbers ofdifferent altered PKS gene clusters and PKS gene products. The number ofmembers in the library is arbitrarily chosen; however, the degrees offreedom outlined above with respect to the variation of starter,extender units, stereochemistry, oxidation state, and chain length isquite large. The polyketide producing colonies can be identified andisolated using known techniques and the produced polyketides furthercharacterized. The polyketides produced by these colonies can be usedcollectively in a panel to represent a library or may be assessedindividually for activity. See, for example,

Colonies in the library are induced to produce the relevant synthasesand thus to produce the relevant polyketides to obtain a library ofcandidate polyketides. The polyketides secreted into the media can bescreened for binding to desired targets, such as receptors, signalingproteins, and the like. The supernatants per se can be used forscreening, or partial or complete purification of the polyketides canfirst be effected. Typically, such screening methods involve detectingthe binding of each member of the library to receptor or other targetligand. Binding can be detected either directly or through a competitionassay. Means to screen such libraries for binding are well known in theart. Alternatively, individual polyketide members of the library can betested against a desired target. In this event, screens wherein thebiological response of the target is measured can be included.

As noted above, the DNA compounds of the invention can be expressed inhost cells for production of proteins and of known and novel compounds.Preferred hosts include fungal systems such as yeast and procaryotichosts, but single cell cultures of, for example, mammalian cells couldalso be used. A variety of methods for heterologous expression of PKSgenes and host cells suitable for expression of these genes andproduction of polyketides are described, for example, in U.S. Pat. Nos.5,843,718 and 5,830,750; WO 01/31035, WO 01/27306, and WO 02/068613; andU.S. patent application Ser. Nos. 10/087,451 (published asUS2002000087451); 60/355,211; and 60/396,513 (corresponding to publishedapplication 20020045220).

Appropriate host cells for the expression of the hybrid PKS genesinclude those organisms capable of producing the needed precursors, suchas malonyl-CoA, methylmalonyl-CoA, ethylmalonyl-CoA, andmethoxymalonyl-ACP, and having phosphopantotheinylation systems capableof activating the ACP domains of modular PKSs. See, for example, U.S.Pat. No. 6,579,695. However, as disclosed in U.S. Pat. No. 6,033,883, awide variety of hosts can be used, even though some hosts natively donot contain the appropriate post-translational mechanisms to activatethe acyl carrier proteins of the synthases. Also see WO 97/13845 and WO98/27203. The host cell may natively produce none, some, or all of therequired polyketide precursors, and may be genetically engineered so asto produce the required polyketide precursors. Such hosts can bemodified with the appropriate recombinant enzymes to effect thesemodifications. Suitable host cells include Streptomyces, E. coli, yeast,and other procaryotic hosts that use control sequences compatible withStreptomyces spp. Examples of suitable hosts that either nativelyproduce modular polyketides or have been engineered so as to producemodular polyketides include but are not limited to actinomyctes such asStreptomyces coelicolor, Streptomyces venezuelae, Streptomyces fradiae,Streptomyces ambofaciens, and Saccharopolyspora erythraea, eubacteriasuch as Escherichia coli, myxobacteria such as Myxococcus xanthus, andyeasts such as Saccharomyces cerevisiae.

In one embodiment, any native modular PKS genes in the host cell havebeen deleted to produce a “clean host,” as described in U.S. Pat. No.5,672,491, incorporated herein by reference. In a variant of thisembodiment, a host cell that produces leptomycin, a leptomycin analog,or a leptomycin derivative in its native state (e.g., Streptomyces sp.ATCC 39366) is engineered so as to delete or inactivate at least onedomain in the leptomycin PKS gene cluster so as to produce a host cellthat no longer produces leptomycin, a leptomycin analog, or a leptomycinderivative. Such a host cell can subsequently be transformed with a genecomprising an active variant of the deleted or inactivated domain, thusrestoring polyketide production by complementation. When the activevariant of the deleted or inactivated domain is derived from a secondPKS gene cluster that produces a polyketide other than leptomycin, suchcomplementation results in the production of a leptomycin analog orderivative. In one embodiment, one or more complete genes (ORFs) of thenative leptomycin synthase are deleted from or inactivated in the hostcell, which is subsequently complemented by transformation withengineered forms of the deleted or inactivated genes (ORFs). Methods forperforming such complementation experiments are known in the art, forexample as described in U.S. Pat. No. 6,505,737 which is incorporatedherein by reference.

In some embodiments, the host cell expresses, or is engineered toexpress, a polyketide “tailoring” or “modifying” enzyme. Once a PKSproduct is released, it is subject to post-PKS tailoring reactions.These reactions are important for biological activity and for thediversity seen among polyketides. Tailoring enzymes normally associatedwith polyketide biosynthesis include oxygenases, glycosyl- andmethyl-transferases, acyltransferases, halogenases, cyclases,aminotransferases, and hydroxylases. In addition to biosyntheticaccessory activities, secondary metabolite clusters often code foractivities such as transport. In the case of leptomycin biosynthesis(FIG. 3), tailoring enzymes are expected to include at least one P450hydroxylase for oxidation of the C24 methyl group to a carboxylic acid.Tailoring enzymes may also be involved in the introduction of thecis-alkene at C8-C9.

Tailoring enzymes for modification of a product of the leptomycin PKS, anon-leptomycin PKS, or a chimeric PKS, can be those normally associatedwith leptomycin biosynthesis or “heterologous” tailoring enzymes.Tailoring enzymes can be expressed in the organism in which they arenaturally produced, or as recombinant proteins in heterologous hosts. Insome cases, the structure produced by the heterologous or hybrid PKS maybe modified with different efficiencies by post-PKS tailoring enzymesfrom different sources. In such cases, post-PKS tailoring enzymes can berecruited from other pathways to obtain the desired compound. Forexample, the tailoring enzymes of the leptomycin PKS gene cluster can beexpressed heterologously to modify polyketides produced bynon-leptomycin synthases or can be inactivated in the Leptomycinproducer.

Alternatively, the unmodified polyketide compounds can be produced inthe recombinant host cell, and the desired modification (e.g.,oxidation) steps carried out in vitro (e.g., using purified enzymes,isolated from native sources or recombinantly produced) or in vivo in aconverting cell different from the host cell (e.g., by supplying theconverting cell with the unmodified polyketide).

It will be apparent to the reader that a variety of recombinant vectorscan be utilized in the practice of aspects of the invention. As usedherein, “vector” refers to polynucleotide elements that are used tointroduce recombinant nucleic acid into cells for either expression orreplication. Selection and use of such vehicles is routine in the art.An “expression vector” includes vectors capable of expressing DNAs thatare operatively linked with regulatory sequences, such as promoterregions. Thus, an expression vector refers to a recombinant DNA or RNAconstruct, such as a plasmid, a phage, recombinant virus or other vectorthat, upon introduction into an appropriate host cell, results inexpression of the cloned DNA. Appropriate expression vectors are wellknown to those of skill in the art and include those that are replicablein eukaryotic cells and/or prokaryotic cells and those that remainepisomal or those which integrate into the host cell genome.

The vectors used to perform the various operations to replace theenzymatic activity in the host PKS genes or to support mutations inthese regions of the host PKS genes may be chosen to contain controlsequences operably linked to the resulting coding sequences in a mannerthat expression of the coding sequences may be effected in anappropriate host. Suitable control sequences include those that functionin eucaryotic and procaryotic host cells. If the cloning vectorsemployed to obtain PKS genes encoding derived PKS lack control sequencesfor expression operably linked to the encoding nucleotide sequences, thenucleotide sequences are inserted into appropriate expression vectors.This can be done individually, or using a pool of isolated encodingnucleotide sequences, which can be inserted into host vectors, theresulting vectors transformed or transfected into host cells, and theresulting cells plated out into individual colonies.

Suitable control sequences for single cell cultures of various types oforganisms are well known in the art. Control systems for expression inyeast are widely available and are routinely used. Control elementsinclude promoters, optionally containing operator sequences, and otherelements depending on the nature of the host, such as ribosome bindingsites. Particularly useful promoters for procaryotic hosts include thosefrom PKS gene clusters that result in the production of polyketides assecondary metabolites, including those from Type I or aromatic (Type II)PKS gene clusters. Examples are act promoters, tcm promoters, spiramycinpromoters, and the like. However, other bacterial promoters, such asthose derived from sugar metabolizing enzymes, such as galactose,lactose (lac) and maltose, are also useful. Additional examples includepromoters derived from biosynthetic enzymes such as for tryptophan(trp), the β-lactamase (bla), bacteriophage lambda PL, and T5. Inaddition, synthetic promoters, such as the tac promoter (U.S. Pat. No.4,551,433), can be used.

As noted, particularly useful control sequences are those whichthemselves, or with suitable regulatory systems, activate expressionduring transition from growth to stationary phase in the vegetativemycelium. The system contained in the plasmid identified as pCK7, i.e.,the actI/actIII promoter pair and the actII-ORF4 (an activator gene), isparticularly preferred. Particularly preferred hosts are those whichlack their own means for producing polyketides so that a cleaner resultis obtained. Illustrative control sequences, vectors, and host cells ofthese types include the modified S. coelicolor CH999 and vectorsdescribed in PCT publication WO 96/40968 and similar strains of S.lividans. See U.S. Pat. Nos. 5,672,491; 5,830,750, 5,843,718; and6,177,262, each of which is incorporated herein by reference.

Other regulatory sequences may also be desirable which allow forregulation of expression of the PKS sequences relative to the growth ofthe host cell. Regulatory sequences are known to those of skill in theart, and examples include those which cause the expression of a gene tobe turned on or off in response to a chemical or physical stimulus,including the presence of a regulatory compound. Other types ofregulatory elements may also be present in the vector, for example,enhancer sequences.

Selectable markers can also be included in the recombinant expressionvectors. A variety of markers are known which are useful in selectingfor transformed cell lines and generally comprise a gene whoseexpression confers a selectable phenotype on transformed cells when thecells are grown in an appropriate selective medium. Such markersinclude, for example, genes which confer antibiotic resistance orsensitivity to the plasmid. Alternatively, several polyketides arenaturally colored, and this characteristic provides a built-in markerfor screening cells successfully transformed by the present constructs.

The various PKS nucleotide sequences, or a mixture of such sequences,can be cloned into one or more recombinant vectors as individualcassettes, with separate control elements or under the control of asingle promoter. The PKS subunits or components can include flankingrestriction sites to allow for the easy deletion and insertion of otherPKS subunits so that hybrid or chimeric PKSs can be generated. Thedesign of such restriction sites is known to those of skill in the artand can be accomplished using the techniques described above, such assite-directed mutagenesis and PCR. Methods for introducing therecombinant vectors of the present invention into suitable hosts areknown to those of skill in the art and typically include the use ofCaCl₂ or other agents, such as divalent cations, lipofection, DMSO,protoplast transformation, conjugation, and electroporation.

Thus, the present invention provides recombinant DNA molecules andvectors comprising those recombinant DNA molecules that encode at leasta portion of the leptomycin PKS and that, when transformed into a hostcell and the host cell is cultured under conditions that lead to theexpression of said leptomycin PKS enzymes, results in the production ofpolyketides including but not limited to leptomycin and/or analogs orderivatives thereof in useful quantities. The present invention alsoprovides recombinant host cells comprising those recombinant vectors.

Suitable culture conditions for production of polyketides using thecells of the invention will vary according to the host cell and thenature of the polyketide being produced, but will be know to those ofskill in the art. See, for example, the examples below and WO 98/27203“Production of Polyketides in Bacteria and Yeast” and WO 01/83803“Overproduction Hosts For Biosynthesis of Polyketides.”

The polyketide product produced by host cells of the invention can berecovered (i.e., separated from the producing cells and at leastpartially purified) using routine techniques (e.g., extraction frombroth followed by chromatography).

The compositions, cells and methods of the invention may be directed tothe preparation of an individual polyketide or a number of polyketides.The polyketide may or may not be novel, but the method of preparationpermits a more convenient or alternative method of preparing it. It willbe understood that the resulting polyketides may be further modified toconvert them to other useful compounds. For example, an ester linkagemay be added to produce a “pharmaceutically acceptable ester” (i.e., anester that hydrolyzes under physiologically relevant conditions toproduce a compound or a salt thereof). Illustrative examples of suitableester groups include but are not limited to formates, acetates,propionates, butyrates, succinates, and ethylsuccinates.

The polyketide product can be modified by addition of a protectinggroup, for example to produce prodrug forms. A variety of protectinggroups are disclosed, for example, in T. H. Greene and P. G. M. Wuts,Protective Groups in Organic Synthesis, Third Edition, John Wiley &Sons, New York (1999). Prodrugs are in general functional derivatives ofthe compounds that are readily convertible in vivo into the requiredcompound. Conventional procedures for the selection and preparation ofsuitable prodrug derivatives are described, for example, in “Design ofProdrugs,” H. Bundgaard ed., Elsevier, 1985.

Similarly, improvements in water solubility of a polyketide compound canbe achieved by addition of groups containing solubilizingfunctionalities to the compound or by removal of hydrophobic groups fromthe compound, so as to decrease the lipophilicity of the compound.Typical groups containing solubilizing functionalities include, but arenot limited to: 2-(dimethylaminoethyl)amino, piperidinyl,N-alkylpiperidinyl, hexahydropyranyl, furfuryl, tetrahydrofurfuryl,pyrrolidinyl, N-alkylpyrrolidinyl, piperazinylamino, N-alkylpiperazinyl,morpholinyl, N-alkylaziridinylmethyl,(1-azabicyclo[1.3.0]hex-1-yl)ethyl, 2-(N-methylpyrrolidin-2-yl)ethyl,2-(4-imidazolyl)ethyl, 2-(1-methyl-4-imidazolyl)ethyl,2-(1-methyl-5-imidazolyl)ethyl, 2-(4-pyridyl)ethyl, and3-(4-morpholino)-1-propyl.

In addition to post synthesis chemical or biosynthetic modifications,various polyketide forms or compositions can be produced, including butnot limited to mixtures of polyketides, enantiomers, diastereomers,geometrical isomers, polymorphic crystalline forms and solvates, andcombinations and mixtures thereof can be produced

Many other modifications of polyketides produced according to theinvention will be apparent to those of skill, and can be accomplishedusing techniques of pharmaceutical chemistry.

Prior to use the PKS product (whether modified or not) can be formulatedfor storage, stability or administration. For example, the polyketideproducts can be formulated as a “pharmaceutically acceptable salt.”Suitable pharmaceutically acceptable salts of compounds include acidaddition salts which may, for example, be formed by mixing a solution ofthe compound with a solution of a pharmaceutically acceptable acid suchas hydrochloric acid, hydrobromic acid, sulfuric acid, fumaric acid,maleic acid, succinic acid, benzoic acid, acetic acid, citric acid,tartaric acid, phosphoric acid, carbonic acid, or the like. Where thecompounds carry one or more acidic moieties, pharmaceutically acceptablesalts may be formed by treatment of a solution of the compound with asolution of a pharmaceutically acceptable base, such as lithiumhydroxide, sodium hydroxide, potassium hydroxide, tetraalkylammoniumhydroxide, lithium carbonate, sodium carbonate, potassium carbonate,ammonia, alkylamines, or the like.

Prior to administration to a mammal the PKS product will be formulatedas a pharmaceutical composition according to methods well known in theart, e.g., combination with a pharmaceutically acceptable carrier. Theterm “pharmaceutically acceptable carrier” refers to a medium that isused to prepare a desired dosage form of a compound. A pharmaceuticallyacceptable carrier can include one or more solvents, diluents, or otherliquid vehicles; dispersion or suspension aids; surface active agents;isotonic agents; thickening or emulsifying agents; preservatives; solidbinders; lubricants; and the like. Remington's Pharmaceutical Sciences,Fifteenth Edition, E. W. Martin (Mack Publishing Co., Easton, Pa., 1975)and Handbook of Pharmaceutical Excipients, Third Edition, A. H. Kibbeed. (American Pharmaceutical Assoc. 2000), disclose various carriersused in formulating pharmaceutical compositions and known techniques forthe preparation thereof.

The composition may be administered in any suitable form such as solid,semisolid, or liquid form. See Pharmaceutical Dosage Forms and DrugDelivery Systems, 5^(th) edition, Lippicott Williams & Wilkins (1991).In an embodiment, for illustration and not limitation, the polyketide iscombined in admixture with an organic or inorganic carrier or excipientsuitable for external, enteral, or parenteral application. The activeingredient may be compounded, for example, with the usual non-toxic,pharmaceutically acceptable carriers for tablets, pellets, capsules,suppositories, pessaries, solutions, emulsions, suspensions, and anyother form suitable for use. The carriers that can be used includewater, glucose, lactose, gum acacia, gelatin, mannitol, starch paste,magnesium trisilicate, talc, corn starch, keratin, colloidal silica,potato starch, urea, and other carriers suitable for use inmanufacturing preparations, in solid, semi-solid, or liquified form. Inaddition, auxiliary stabilizing, thickening, and coloring agents andperfumes may be used.

EXAMPLES

The following Examples are intended to illustrate, but not limit, thescope of the invention.

Example 1 Gene Library Construction

Growth of Organism and Extraction of Genomic DNA

For genomic DNA extraction, a spore stock of Streptomyces sp ATCC 39366(obtained from the American Type Culture Collection, Manassas, Va.) wasinoculated into 35 ml of liquid R5 medium three days and grown in 30° C.A 10 ml portion of the cell suspension was centrifuged 5,000×g. Thepellet was suspended into 3.5 ml of buffer I (Tris, 50 mM, pH7.5; 20 mMEDTA, 150 μg/ml RNase (Sigma-Aldrich) and 1 mg/ml of lysozyme (Sigma)).After incubation of the mixture at 37° C. for about 30 min, the saltconcentration was adjusted by adding 850 μl of 5 M NaCl solution, thenthe mixture was extracted two times with phenol:chloroform:isoamylalcohol (25:24:1, vol/vol) with gentle agitation followed bycentrifugation for 10 min at 12,000×g. The genomic DNA in thesupernatant was precipitated with 1 vol of isopropanol and redissolvedin 800 μl of water.

Genomic Library Preparation

Approximately 10 μg of genomic DNA was partially digested with Sau3A1 (aseries digestions with different dilutions of the enzyme) and thedigested DNAs were run on an agarose gel with DNA standards. One of theconditions used was found to have generated fragments of size 30-45 kb.The DNA from this digestion was ligated with pSuperCos-1 (Stratagene),pre-linearized with BamHI and XbaI and the ligation mixture was packagedusing a Gigapack XIII (Stragene) in vitro packaging Kit and the mixturewas subsequently used for infection of Escherichia coli DH5α employingprotocols supplied by the manufacturer.

Identification of Leptomycin Biosynthetic Gene Cluster

To find the gene cluster for leptomycin biosynthesis, cosmids from 475E. coli transductants resulted from the above ligation mixture weresequenced using convergent primersT7cos (5′-CATAATACGACTCACTATAGGG) (SEQID NO:10) and T3cos-1 (5′-TTCCCCGAAAAGTGCCAC) (SEQ ID NO:11). AfterBLAST analysis, the sequences revealed that 4 cosmids carried DNAinserts with both ends encoding type I PKS (polyketide synthetase)genes. Restriction analysis of these four cosmids with BamHI showed 3cosmids having overlapping inserts; the fourth cosmid (pKOS279-125.2L78)was distinct. Cosmid pKOS279-125.2L78 and pKOS279-125.3L71 from the 3overlapping cosmids were sequenced. The incomplete sequences ofpKOS279-125.2L78 revealed 6 complete modules and three incompletemodules.

From the 475 cosmids sequenced, also it was found that 16 cosmids carryinserts with PKS genes at one of their ends. While the above cosmidswere under sequenced, DNA fragments encoding PKS genes from these 16cosmids were pulled out by PCR and labeled with DIG (digoxigenin,Roche). The DIG-labeled PCR products were used to screen about 2000 E.coli transductants resulting from the ligation mixture of SuperCos-1 andpartially-digested genomic DNA from the leptomycin producer. The in situhybridization revealed up 89 positive transductants, and the cosmids inthese clones were verified to contain PKS inserts by sequencing usingT7cos and T3cos-1 primers (SEQ ID NO:57 and 58, respectively).

After DNA sequences of pKOS279-125.2L78 were available, these endsequences were analyzed using BLAST. DNA Blast revealed 3 interestingcosmids (pKOS279-128.PF26, pKOS279-128.PF27 and pKOS279-128.PF48. These3 cosmids all have inserts extending to cover upstream of KR1ACP1 andreaching non-PKS genes (see FIG. 4).

All publications and patent documents cited herein are incorporatedherein by reference as if each such publication or document wasspecifically and individually indicated to be incorporated herein byreference.

Although the present invention has been described in detail withreference to specific embodiments, those of skill in the art willrecognize that modifications and improvements are within the scope andspirit of the invention. Citation of publications and patent documentsis not intended as an admission that any such document is pertinentprior art, nor does it constitute any admission as to the contents ordate of the same. The invention having now been described by way ofwritten description, those of skill in the art will recognize that theinvention can be practiced in a variety of embodiments and that theforegoing description are for purposes of illustration and notlimitation of the following claims.

1. An isolated DNA molecule comprising a polynucleotide having anucleotide sequence that is at least 95.0% identical to 58243 to 64170of SEQ ID NO:3, wherein said polynucleotide encodes a polypeptide havingthioesterase activity.
 2. An isolated DNA molecule comprising apolynucleotide sequence encoding SEQ ID NO:7.
 3. The isolated DNAmolecule of claim 2, wherein said polynucleotide comprises nucleotides58243 to 64170 of SEQ ID NO:3.
 4. A recombinant polyketide synthase(PKS) comprising the isolated nucleic acid molecule of claim
 2. 5. Anisolated recombinant host cell comprising the PKS of claim
 4. 6. Arecombinant vector comprising the isolated nucleic acid molecule ofclaim
 2. 7. An isolated recombinant host cell comprising the vector ofclaim
 6. 8. A method of making an isolated polypeptide comprising: (a)culturing the isolated recombinant host cell of claim 5 or claim 7 underconditions such that said polypeptide is expressed; and (b) recoveringsaid polypeptide.
 9. The isolated DNA molecule of claim 2, wherein saidnucleic acid sequence further comprises at least a portion of a PKSsequence.
 10. The isolated DNA molecule of claim 9, wherein said nucleicacid sequence further comprises at least a portion of a second PKSsequence.
 11. An isolated DNA molecule comprising the completecomplementary sequence of the polynucleotide provided in claim 2.